Application Definitions

Frequently Asked Questions (FAQs)

What is Airborne GeophysWeb?

Airborne GeophysWeb is a compilation of information about publicly available airborne geophysical surveys conducted in Alaska since 1993 by the Division of Geological & Geophysical Surveys (DGGS), U.S. Geological Survey (USGS), and Bureau of Land Management (BLM). The application contains a text- and map-based search interface to make geophysical survey information easily accessible. The application provides access to DGGS's geophysical publications where users may view and download data and maps for free.

What types of data does Airborne GeophysWeb contain?

The application contains a data catalog of publicly available airborne geophysical data flown in Alaska from 1993 to the present. All data in this publication, except for small blocks of older data, were acquired with GPS technology. Survey types included are aeromagnetic, frequency-domain electromagnetic, and radiometric data. Currently all data were acquired by helicopter except for the fixed-wing magnetic surveys. The compilation includes basic survey parameters and information, a spatial footprint, and a representative image of each dataset.

How do I obtain the geophysical data and maps?

Click on the "Get Data" link that appears in either the search results or the survey details pop-up box on the map. The summary page for each survey will provide any digital data available for download at the top. It will also include all related geophysical publications links with maps in PDF format for the survey. Any related geologic publications are also displayed.

If the survey's digital data is not yet available for download, please contact us to order the data on DVD. Please bear with us as we are prepare the legacy geophysics digital data to be distributed online.

Where can I find information on older, regional aeromagnetic data?

Most of the older, publicly available aeromagnetic data for Alaska was flown in the 1960's and 1970's in a cooperative venture between the USGS and DGGS. Individual surveys are available at the following links below.

Searching in Airborne GeophysWeb

Airborne GeophysWeb Search Philosophy

Airborne geophysical survey records may be queried by geographic area, specific text, or a combination of area and text. All surveys have an associated spatial footprint that has been generalized for faster application performance. Data images are selected for their display properties, and are not intended for interpretation or analysis.

Geographic-based searches

An Area of Interest (AOI) search is available from the map interface. Click on the icon (active icon is yellow) and click and drag your mouse to define your area of interest. Geographic searches will often return spatial objects outside of the AOI selected, because a given record may be associated with multiple spatial objects, and all spatial objects for a record are displayed on the map.

Text-based searches: Basic Search Bar

The application is designed to provide results for broad and narrowly focused searches. The basic search bar above the map allows for robust queries of multiple single terms, phrases, term modifiers. The default behavior of the basic search bar is to select records on a "best match" basis. For example, a search for...

Fairbanks H-Mag 2006

...will only return records that have all three terms, with any of the fields searched. The basic search bar searches the following fields:

Airborne GeophysWeb Layer Options

Each "layer" represents a geophysical survey type, except the Current Surveys which represents the survey areas where data are currently being collected or processed for publication. Use the Image radio buttons to display each survey's geophysical data image for the individual layer. The images are generalized representations of the downloadable or orderable datasets. Only one layer of images can be displayed at one time. Use the Border check boxes to display and highlight the vector border of each survey area for that individual layer or to filter the survey types that are returned in the results. Borders on this map are generalized and may not fit the image area exactly on the edges. All the borders are displayed by default.

Text-based searches: Additional Parameters

The side panel allows users to narrow searches with additional specific fields. These parameters are more restrictive in the number of fields they query, and can help narrow down a search considerably. A search conducted on one or more fields in the additional parameters section or the basic search bar will only return records that match all of the parameters entered. For example, a search conducted on...

Basic search bar: H-MagSurvey Name: FairbanksYear(s) Flown: 2002-2006

...will only return surveys named "Fairbanks" flown from 2002 to 2006 of H-Mag survey type.

Below is information on the additional search parameters with hints for acheiving sucessful search results. Please see the Application Definitions for further descriptions on other fields appearing in the application.

Additional Parameters

Definition and Search Hints

Survey Name

The common name associated with the general geographical area where the survey was flown. Enter the beginning letters in this field to auto-generate a valid list of matching survey names.

Year(s) Flown

The year(s) during which the survey was flown. To search a single or range of years when surveys were flown, the From and To fields must both be entered. To search a single year, enter the same year value in both the From field and the To field.

Nominal AGL (feet)

The nominal altitude in feet above ground level (AGL) of the geophysical platform (helicopter or airplane). To search a single or range of heights, the From and To fields must both be entered. To search a single height, enter the same value in both the From field and the To field.

Line spacing (feet)

The nominal distance between traverse lines (main lines of the survey). A list of values is provided and translated into miles.

Agency

The organization(s) responsible for the survey.

Quadrangle(s)

Searches for geophysical surveys covered by 1:250,000-scale USGS quadrangles. More than one quadrangle may be selected. If more than one quadrangle is selected, the search will find surveys covering any of the quadrangles named. For example, if both "Fairbanks" and "Anchorage" quadrangles are selected, some surveys returned will only cover Fairbanks and some will only cover Anchorage.

Application Definitions

Search Results Fields

The fields below appear in the search results under the map after entering successful search parameters.

Note: Information about older data that were incorporated into more recent surveys are shown by values in parentheses. Older data always follows the newer data, e.g. 1993 (1987).

Display Name

CSV Column Name

WFS Attribute

Definition

Survey Name

Survey Name

SURVEYNAME

Each polygon represents a survey (or survey block) for which the data and acquisition parameters are described in this application. The survey name is typically the name used for the published survey. Some names are abbreviated, for example 'NE Fairbanks', and some denote the survey name used for publishing and a particular block in that survey, for example 'Stikine - Groundhog Basin'.

Survey Type

Survey Type

SURVEYTYPE

The abbreviation of the data type for the individual record. Survey areas may have multiple records corresponding to different data types. Valid values for searching are:
H-Mag, FW-Mag, H-FEM, Rad, and New.

H-Mag = Helicopter Magnetics

FW-Mag = Fixed-Wing Magnetics

H-FEM = Helicopter Frequency-Domain Electromagnetics

Rad = Helicopter Radiometrics

New = Current Surveys being flown or processed

Additional data types for this survey are shown in the column "Additional Survey Types".

Additional Survey Types

Additional Survey Types

ADDLSURVEY

The types of survey data available for this polygon other than main data type of the currently selected record (indicated in "Survey Type").

Year Flown

Years(s) Flown

YEARFLOWN

The year(s) during which the survey was flown. A year followed by a more recent year indicates that the agency flew and acquired those data both years, commonly but not always under one contract. A year followed by an older year(s) indicates data from the older year(s) were incorporated into the newest data and came from other sources.

The nominal distance in miles between traverse lines (main lines of the survey).

Agency

Agency

AGENCY

The organization(s) responsible for the survey. For 'BLM and DGGS' values, BLM was responsible for funding and location of the survey; DGGS was responsible for contracting, quality control, and publishing the data.

Survey Details Pop-Up Fields

The fields below appear in a pop-up balloon when clicking on a polygon within the map or when clicking on the Survey Name link in the search results.

Note: Information about older data that were incorporated into more recent surveys are shown by values in parentheses. Older data always follows the newer data, e.g. 1993 (1987). The "Comments" field may also include information about older surveys.

Display Name

CSV Column Name

WFS Attribute

Definition

Survey Name

Survey Name

SURVEYNAME

Each polygon represents a survey (or survey block) for which the data and acquisition parameters are described in this application. The survey name is typically the name used for the published survey. Some names are abbreviated, for example 'NE Fairbanks', and some denote the survey name used for publishing and a particular block in that survey, for example 'Stikine - Groundhog Basin'.

Quadrangle(s)

Quadrangle(s)

QUADS

The U.S. Geological Survey 1:250,000-scale quadrangle(s) partly covered by the survey. In rare cases, a survey covers an entire quadrangle.

Agency

Agency

AGENCY

The organization(s) responsible for the survey. For 'BLM and DGGS' values, BLM was responsible for funding and location of the survey; DGGS was responsible for contracting, quality control, and publishing the data.

Survey Type

Survey Type

SURVEYTYPE

The abbreviation of the data type for the individual record. Survey areas may have multiple records corresponding to different data types. Valid values for searching are: H-Mag, FW-Mag, H-FEM, Rad, and New.

H-Mag = Helicopter Magnetics

FW-Mag = Fixed-Wing Magnetics

H-FEM = Helicopter Frequency-Domain Electromagnetics

Rad = Helicopter Radiometrics

New = Current Surveys being flown or processed

Additional data types for this survey are shown in the column "Additional Survey Types".

Additional Survey Types

Additional Survey Types

ADDLSURVEY

The types of survey data available for this polygon other than main data type of the currently selected record (indicated in "Survey Type").

Year Flown

Years(s) Flown

YEARFLOWN

The year(s) during which the survey was flown. A year followed by a more recent year indicates that the agency flew and acquired those data both years, commonly but not always under one contract. A year followed by an older year(s) indicates data from the older year(s) were incorporated into the newest data and came from other sources.

Data Release(s)

Data Release(s)

YRRELEASE

The year(s) when the geophysical data were released to the public. In the future, the year(s) of related geophysical publications will be added to this field for all DGGS surveys. The year when significant data format changes or major map improvements are made, appears in "Major Publication Revision(s)".

Major Publication Revision(s)

Major Publication Revision(s)

MAJPUBREDO

The year(s) when significant changes were made to the geophysical publication, such as a data format change or significant map improvements.

The nominal distance in miles between traverse lines (main lines of the survey).

Line-mi Flown

Line-mi Flown

LINE_MI

The sum total length (in miles) of the traverse and tie lines for the survey or block, as appropriate. If older data are incorporated into the dataset, the value in this field includes those line miles, unless noted in comments.

CSV Columns / Web Feature Service (WFS) Attributes

The fields below appear in the comma-separated value (.CSV) file from the Download CSV link and also as the Web Feature Service (WFS) attributes for this dataset. The WFS link will be available on the citation page for DDS 2.

Note: Information about older data that were incorporated into more recent surveys are shown by values in parentheses. Older data always follows the newer data, e.g. 1993 (1987). The line spacing for the tie lines is not included at this time, but will appear at a later date in column "Tie Line Spacing". The "Comments" field may also include information about older surveys.

Display Name

CSV Column Name

WFS Attribute

Definition

Survey Name

Survey Name

SURVEYNAME

Each polygon represents a survey (or survey block) for which the data and acquisition parameters are described in this application. The survey name is typically the name used for the published survey. Some names are abbreviated, for example 'NE Fairbanks', and some denote the survey name used for publishing and a particular block in that survey, for example 'Stikine - Groundhog Basin'.

Survey Type

Survey Type

SURVEYTYPE

The abbreviation of the data type for the individual record. Survey areas may have multiple records corresponding to different data types. Valid values for searching are: H-Mag, FW-Mag, H-FEM, Rad, and New. Additional data types for this survey are shown in the column "Additional Survey Types".

Additional Survey Types

Additional Survey Types

ADDLSURVEY

The types of survey data available for this polygon other than main data type of the currently selected record (indicated in "Survey Type").

Year Flown

Years(s) Flown

YEARFLOWN

The year when the survey was flown. A year followed by a more recent year indicates that the agency flew and acquired those data both years, commonly but not always under one contract. A year followed by an older year(s) indicates data from the older year(s) were incorporated into the newest data and came from other sources.

The nominal distance in miles between traverse lines (main lines of the survey).

Agency

Agency

AGENCY

The organization(s) responsible for the survey. For 'BLM and DGGS' values, BLM was responsible for funding and location of the survey; DGGS was responsible for contracting, quality control, and publishing the data.

Image Source

Image Source

IMAGE_SRC

Image source, either single grids or a merged grid containing several surveys. Sometimes multiple geophysical blocks are grouped together in order to make a combined data product (image). This field tracks which surveys compose the image.

Quadrangle(s)

Quadrangle(s)

QUADS

The U.S. Geological Survey 1:250,000-scale quadrangle(s) partly covered by the survey. In rare cases, a survey covers an entire quadrangle.

Data Release(s)

Data Release(s)

YRRELEASE

The year(s) when the geophysical data were released to the public. In the future, the year(s) of related geophysical publications will be added to this field for all DGGS surveys. The year when significant data format changes or major map improvements are made, appears in "Major Publication Revision(s)".

Major Publication Revision(s)

Major Publication Revision(s)

MAJPUBREDO

The year(s) when significant changes were made to the geophysical publication, such as a data format change or significant map improvements.

Operator

Operator

OPERATOR

The airborne geophysical services company that conducted the survey.

EM Equipment

EM Equipment

EM_EQUIP

The system used to collect electromagnetic (EM) data.

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Flight Line Direction

TRAV_DIR

The azimuth of traverse lines (main data collection lines). Azimuth is the angle in degrees from north in a clockwise direction.

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Mag Height (meters)

MAG_HEIGHT

The nominal altitude of the magnetic sensor above ground level in meters.

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EM Height (meters)

EM_HEIGHT

The nominal altitude of the electromagnetic (EM) sensor above ground level in meters.

Area (sq mi)

Area (sq mi)

SURVEYAREA

The size of the survey area in square miles.

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Line-km Flown

LINE_KM

The sum total length (in kilometers) of the traverse and tie lines for the survey or block, as appropriate. If older data are incorporated into the dataset, the value in this field includes those line kilometers, unless noted in comments.

Line-mi Flown

Line-mi Flown

LINE_MI

The sum total length (in miles) of the traverse and tie lines for the survey or block, as appropriate. If older data are incorporated into the dataset, the value in this field includes those line miles, unless noted in comments.

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Image Information

IMAGEINFO

To be defined when images are included with the polygons.

Comments

Comments

COMMENTS

Any additional information regarding the survey.

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Tie Line Spacing (mi)

TIE_LINE

The distance between tie lines measured in miles. Tie lines are typically perpendicular to traverse lines.

Image Maximum

Image Maximum

IMAGE_MAX

To be defined when images are included with the polygons.

Image Minimum

Image Minimum

IMAGE_MIN

To be defined when images are included with the polygons.

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Purpose

PURPOSE

The principal reason for collecting the geophysics data, such as determining resource potential for a geographical area, infrastructure, etc. Examples are: Minerals, Energy, and Infrastructure.

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Program

PROGRAM

The agency program that sponsored the survey, such as DGGS's Alaska Airborne Geophysical & Mineral Inventory program (AGGMI).

Glossary

The definitions given in this glossary refer to the common terminology as used in airborne geophysics. Modified from: "Fugro Glossary of Airborne Geophysical Terms"; Version 1.8, February, 2012; Greg Hodges, Chief Geophysicist; Fugro Airborne Surveys, Toronto

analytic signal:

The total amplitude of all the directions of magnetic gradient. Calculated as the sum of the squares.

apparent-:

The physical parameters of the earth measured by a geophysical system are normally expressed as apparent, as in "apparent resistivity". This means that the measurement is limited by assumptions made about the geology in calculating the response measured by the geophysical system. Apparent resistivity calculated with HEM, for example, generally assumes that the earth is a homogeneous half-space, not layered.

coaxial coils:

[CX] Coaxial coils in an HEM system are in the vertical plane, with their axes horizontal and collinear in the flight direction. These are most sensitive to vertical conductive objects in the ground, such as thin, steeply dipping conductors perpendicular to the flight direction. Coaxial coils generally give the sharpest anomalies over localized conductors. (See also coplanar coils)

coil:

A multi-turn wire loop used to transmit or detect electromagnetic fields. Time varying electromagnetic fields through a coil induce a voltage proportional to the strength of the field and the rate of change over time.

conductor:

Used to describe anything in the ground more conductive than the surrounding geology. Conductors are most often clays or graphite, or hopefully some type of mineralization, but may also be man-made objects, such as fences or pipelines.

coplanar coils:

[CP] In HEM, the coplanar coils lie in the horizontal plane with their axes vertical, and parallel. These coils are most sensitive to massive conductive bodies, horizontal layers, and the halfspace.

counts (per second):

The number of gamma-rays detected by a gamma-ray spectrometer. The rate depends on the geology, but also on the size and sensitivity of the detector.

depth of exploration:

The maximum depth at which the geophysical system can detect the target. The depth of exploration depends very strongly on the type and size of the target, the contrast of the target with the surrounding geology, the homogeneity of the surrounding geology, and the type of geophysical system. One measure of the maximum depth of exploration for an electromagnetic system is the depth at which it can detect the strongest conductive target -- generally a highly conductive horizontal layer.

fiducial, or fid:

Timing mark on a survey record. Originally these were timing marks on a profile or film; now the term is generally used to describe 1-second interval timing records in digital data, and on maps or profiles.

frequency domain:

An electromagnetic system which transmits a harmonic primary field that oscillates over time (e.g. sinusoidal), inducing a similarly varying electrical current in the ground. These systems generally measure the changes in the amplitude and phase of the secondary field from the ground at different frequencies by measuring the in-phase and quadrature phase components. See also time-domain.

HEM:

Helicopter ElectroMagnetic, This designation is most commonly used for helicopter-borne, frequency-domain electromagnetic systems. At present, the transmitter and receivers are normally mounted in a bird carried on a sling line beneath the helicopter.

HFEM:

Helicopter Frequency-domain ElectroMagnetic, This designation is used for helicopter-borne, frequency-domain electromagnetic systems. Formerly most often called HEM.

HTEM:

Helicopter Time-domain ElectroMagnetic, This designation is used for the new generation of helicopter-borne, time-domain electromagnetic systems.

mag:

common abbreviation for magnetic.

magnetic:

("mag") a survey measuring the strength of the earth's magnetic field, to identify geology and targets by their effect on the field.

International Geomagnetic Reference Field (IGRF):

An approximation of the smooth magnetic field of the earth, in the absence of variations due to local geology. Once the IGRF is subtracted from the measured magnetic total field data, any remaining variations are assumed to be due to local geology. The IGRF also predicts the slow changes of the field up to five years in the future.

radioelements:

This normally refers to the common, naturally-occurring radioactive elements: potassium (K), uranium (U), and thorium (Th). It can also refer to man-made radioelements, most often cobalt (Co) and cesium (Cs)

radiometric:

Commonly used to refer to gamma ray spectrometry.

radon:

A radioactive daughter product of uranium and thorium, radon is a gas which can leak into the atmosphere, adding to the non-geological background of a gamma-ray spectrometric survey.

resistivity:

The strength with which the earth or a geological formation resists the flow of electricity, typically the flow induced by the primary field of the electromagnetic transmitter. Normally expressed in ohm-metres, it is the reciprocal of conductivity.

time-domain:

Electromagnetic system which transmits a pulsed, or stepped electromagnetic field. These systems induce an electrical current (eddy current) in the ground that persists after the primary field is turned off, and measure the change over time of the secondary field created as the currents decay. See also frequency-domain.

traverse line:

A normal geophysical survey line. Normally parallel traverse lines are flown across the property in spacing of 50 m to 500 m, and generally perpendicular to the target geology. Also called a flight line.